1. Field of the Invention
The present invention relates to liquid alcohol-terminated copolyesters obtained from 1,4-butanediol and mixed aliphatic dicarboxylic acids (or anhydride or ester thereof) and to their use as plasticizers for vinyl resins, particularly polyvinyl chloride (PVC).
2. Description of the Prior Art
Copolyester plasticizers for vinyl resins used in the manufacture of pressure sensitive electrical tapes must be resistant to hydrocarbon extraction, since adhesive backings are customarily applied with hydrocarbon diluents, and should impart good low temperature flexibility characteristics to the resin composition. Also, for ease of handling, the copolyesters are preferably liquids at room temperature and, more preferably, down to about 20.degree. C. or below. This feature, while not necessarily related to the performance characteristics of the product, is an important consideration for commercial operations where the plasticizer is typically held in bulk storage tanks. In most instances, these tanks are not heated since this adds additional cost to the operation and can adversely affect the servicelife of the product.
Alcohol-terminated copolyesters derived from C.sub.6-9 aliphatic dicarboxylic acids and mixtures of 1,4-butanediol and propylene glycol were developed to meet these requirements and have been extensively used throughout the industry. Both the C.sub.6-9 discarboxylic acid and the 1,4-butanediol/propylene glycol mixture were considered to be essential to obtain a copolyester having an acceptable balance of properties.